Estimating the Annual Exceedance Probability of Water Levels and Wave Heights from High Resolution Coupled Wave-Circulation Models in Long Island Sound

Chang Liu,Yaprak Onat,James O’Donnell,Alejandro Cifuentes-Lorenzen,Yan Jia,Amin Ilia,Todd Fake,Grant Mccardell

doi:10.3390/jmse8070475

Abstract

Accurately estimating the probability of storm surge occurrences is necessary for flood risk assessments. This research models Long Island Sound using a coupled coastal circulation and wave model (FVCOM-SWAVE) to hindcast the 44 highest storms between 1950–2018 and fitted Poisson-GPD distributions to modelled water levels and wave heights. Floodwater elevations and significant wave heights for 10% (1/10), 3% (1/30), 2% (1/50), and 1% (1/100) annual exceedance probabilities are provided for all Connecticut coastal towns. The results show that both water levels and their corresponding return intervals are higher along the western coast of Connecticut than the eastern coast, whereas significant wave heights increase eastward. Comparing our model results with those from the North Atlantic Coast Comprehensive Study (NACCS) shows that the mean NACCS results are higher for water levels and lower for significant wave heights for longer return periods. Likewise, the Federal Emergency Management Agency (FEMA) results in large errors compared to our results in both eastern and western coastal Connecticut regions. In addition to evaluating historical risks, we also added a sea-level height offset of 0.5 m for 2050 estimates in order to examine the effect of rising sea-levels on the analysis. We find that sea-level rise reduces the return period of a 10-year storm to two years. We advise periodically updating this work as improved sea-level rise projections become available.

Highlights

Storm flooding is a destructive event that damages infrastructure, especially in coastal areas with low elevations
Modeled results from Finite Volume Community Ocean Model (FVCOM)-SWAVE were compared to observations from Kings Point, Bridgeport, New Haven, New London, and Montauk tide gauges for water levels associated with Hurricanes Irene and Sandy (Figure 2)
The results presented here summarize the Generalized Pareto Distributions (GPD) analysis results with return interval estimates for storm surges and waves

Summary

Introduction

Storm flooding is a destructive event that damages infrastructure, especially in coastal areas with low elevations. Damages caused by increased water levels from historic storm surges and waves in low-lying areas can be used in order to estimate the potential for future damage from similar events. O’Donnell [6] emphasized that storm-related flood risks would increase as the sea-level rose. Storm-induced flooding risk assessments should include the effect of sea-level rise, and we use an upper bound of 50 cm sea-level rise by 2050 for Connecticut [6]. Extratropical storms called Nor’easters are the dominant storm source and generate large sea level anomalies in the western Sound due to the sea-surface height setup on the adjacent continental shelf [21]. The shelf morphology causes different return periods for similar water level anomalies in the western and eastern LIS.

Objectives

Methods

Results

Conclusion